In recent years, due to increase in awareness of energy saving, there have been proposed a large number of permanent magnet electric motors configured to use rare-earth permanent magnets having high coercivity in a rotator, to thereby realize high efficiency. However, the rare-earth permanent magnets are expensive, which leads to increase in cost of the electric motor. Therefore, in a rotator of a related-art general interior permanent magnet motor, sintered ferrite magnets are used instead of the rare-earth permanent magnets. When the sintered ferrite magnets are used instead of the rare-earth permanent magnets as described above, the residual flux density, which represents the magnitude of the magnetic force, is reduced to about ⅓. In order to compensate for the lack of torque due to the reduction in magnetic force, it is necessary to arrange, inside the rotator core, sintered ferrite magnets whose surface areas of the permanent magnets are increased as much as possible. Further, reluctance torque is actively used in addition to the torque caused by the permanent magnets. In this manner, the lack of the magnetic force due to the sintered ferrite magnets can be compensated for.
For example, in Patent Literature 1, the following rotator of the interior permanent magnet motor is disclosed. The rotator of the interior permanent magnet motor includes a laminated core and a shaft, and the laminated core includes a plurality of arc-shaped permanent magnets and a plurality of punched holes for accommodating the permanent magnets therein. The plurality of punched holes are formed at a rate of one per pole. Further, each of the plurality of punched holes is arranged so that the protruded portion side of the arc is directed toward the rotator center.
Further, in the interior permanent magnet motor disclosed in Patent Literature 2, permanent magnets each shaped so that the thicknesses of circumferential end portions thereof are different from each other are used. Each of the permanent magnets is arranged so that the end portion having a smaller thickness is positioned on the front side in the rotational direction, and the end portion having a larger thickness is positioned on the rear side in the rotational direction. With such a configuration, an inductance is increased while suppressing the increase in magnetic flux, which causes a counter torque. With this, the reluctance torque is effectively increased, and the increase in core loss is suppressed.
Further, in the interior permanent magnet motor disclosed in Patent Literature 3, a pair of permanent magnet slots, which forms one pole, is arranged in a V-shape in an outer peripheral portion of the rotator core, and the permanent magnets are embedded into the respective permanent magnet slots. That is, in the rotator core, two homopolar permanent magnets are embedded in a V-shape per pole. The thickness of each of the permanent magnets increases from an end portion on the radially inner side of the rotator core, which corresponds to the center part of the V-shape, toward an end portion on the radially outer side of the rotator core, which corresponds to the right or left end portion of the V-shape. Further, curved portions are formed at both end portions of each of the permanent magnets.